Only on rare occasion.
Source: wiktionary
On occasion
Synonyms for "on occasion" (12 found)
Ranked by relevance and common usage.
Closest matches (3)
Adverb(2 words)
at timesfrom time to time
Strong matches (3)
Adverb(2 words)
now and againnow and then
Related words (6)
Adverb(2 words)
occasionallyonce in a while
Sample sentences
2 total sentences available.
It is not in itself surprising that a genuine advance of knowledge should in this manner become on occasion a source of new error.
Source: wiktionary